Generational disease prevalence may be tied to obesity

Action Points

A longitudinal study of arthritis prevalence in the Canadian population, dating back to people born 1935-1944, demonstrates that each succeeding generation had a higher prevalence of arthritis.

Note that increasing arthritis prevalence may be linked to rising obesity rates since severely obese people were 2.5 times more likely to report arthritis than people with normal BMI.

Young generations reported arthritis at an earlier age, which may be linked to rising obesity rates, according to a Canadian study.

Using people born during World War II as a benchmark (1935-1944), the odds ratio for arthritis in generation Xers (1965-1972) was 3.20 (95% CI 2.50-4.10), while for younger baby boomers (1955-1964), the OR was 2.14 (95% CI 1.76-2.60). For older baby boomers 1945-1954, it was 1.48 (95% CI 1.25-1.76), reported Elizabeth Badley, PhD, of the Dalla Lana School of Public Health at the University of Toronto, and colleagues.

They also found that severely obese people were 2.5 times more likely to report arthritis than people with normal (BMI), they wrote in Arthritis Care & Research.

The authors examined the Canadian longitudinal National Population Health Survey (NPHS) from 1994 to 2011 (n=8,817 at baseline). NPHS questionnaires were administered every 2 years and assessed, among other things, self-reported chronic conditions like arthritis that had been diagnosed by a healthcare professional.

In each birth cohort, the proportion of people who reported arthritis increased from 1994 to 2011, the authors noted.

Reviewing data across the 18-year span, they compared how prevalent arthritis was in succeeding generations, and found that, at the same ages, those in each successive cohort were more likely to report arthritis than their predecessors.

"More recent cohorts had successively greater prevalence of arthritis. Significant cohort-BMI and age-BMI interactions indicated an earlier age of arthritis onset for obese individuals than those of normal weight," the authors wrote.

Badley's group also saw trends between socioeconomic status and arthritis. People with higher education were less likely to report arthritis (OR 0.54, 95% CI 0.40-0.74) as were those with higher income (OR 0.65, 95% CI 0.57-0.74.)

Non-smokers (OR 0.57, 95% CI 0.51-0.66) also were less likely to report arthritis than people who currently smoked.

"In every cohort, it seems that the benefits of societal changes in increasing income, education, and smoking cessation on potentially reducing the prevalence of arthritis have been largely offset by the effect of increasing obesity over time," the researchers noted. "In other words, had it not been for the increasing prevalence of obesity over time, the prevalence of arthritis might have declined in all cohorts, with the corollary that our understanding of the impact of BMI on arthritis prevalence trends is likely to be an underestimate."

They speculated that outside factors, including increased awareness of arthritis, may have contributed to these findings. Since the early 1990s, drug companies have advertised more extensively in U.S. media, reaching audiences in Canada. And as young people became more educated, they might have gained greater health literacy, thus becoming more aware of arthritis.

Increasing levels of physical activity and exercise in Canada could have been a factor, too. Active people may have been more aware of joint symptoms or could have experienced exercise-related musculoskeletal injuries that contributed to OA.

The generational differences show that arthritis education needs to reach young and middle-aged adults, the authors emphasized.

"Not only was the cohort effect of higher arthritis prevalence more marked in those who were obese compared to those of normal weight, in all cohorts the age of onset of arthritis in obese individuals was earlier," they wrote. "This has implications for the targeting of public health messages for the control and management of arthritis."

Study limitations were attrition and self-reporting. Attrition occurred due to dropouts and death, especially in the World War II cohort, although sensitivity analyses showed these losses did not alter the study's conclusions, the authors explained.

The authors noted that although the NPHS questionnaire asked about arthritis in general, it is likely their findings reflected osteoarthritis, given its prevalence.

The study was funded by a grant from the Canadian Institutes of Health Research.

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